Reaction mechanism studies will be continued with a number of flavoproteins, including the following: p-hydroxybenzoate hydroxylase, melilotate hydroxylase, lactate monoxygenase, D-lactate dehydrogenase, lipoyl dehydrogenase, D-amino acid oxidase, and xanthine oxidase. The aim of the work is the elucidation of the role of the flavin coenzyme in a variety of reactions of different types; the role of flavin peroxides in hydroxylation reactions, the role of covalent intermediates of flavin and substrate in dehydrogenation reactions, the participation and role of charge-transfer complexes and flavin radicals in catalysis. Emphasis will also be given to the elucidation of the individual steps involved in dehydrogenation reactions, including those possibly involving carbanion intermediates. Where appropriate, use will be made of chemically modified flavins introduced into the enzyme in place of the natural coenzyme, with the aim of changing rates of individual steps in catalysis, and the consequent possibility of characterizing intermediates which have so far escaped detection. Research will also be continued actively on the photochemistry of flavins and deazaflavins, in particular on the mechanism and utility of photo reduction reactions catalysed by deazaflavins. BIBLIOGRAPHIC REFERENCES: Purification of Intact Old Yellow Enzyme Using an Affinity Matrix for the Sole Chromatographic Step. A.S. Abramovitz and V. Massey, J. Biol. Chem. 251 (1976) 5321-5326. Interaction of Phenols with Old Yellow Enzyme. Physical Evidence for Charge Transfer Complexes. A.S. Abramovitz and V. Massey, J. Biol. Chem. 251 (1976) 5327-5336.